Martinez rates the dynamic midfielder as a "phenomenal talent" and "a superstar in our eyes already" but believes he is yet to realise his full potential.

"Ross is probably the best English talent I have ever seen, but he is not the finished article yet and you need to be very careful," Martinez told The Guardian. "It's our duty to protect him and I know Everton is the perfect place for him for the next 12 months.

"In football obviously you can never speak about the future. Obviously we need to come along and try to get into the top-four positions to offer players like Ross the next stage of their development. Ross is delighted at Everton and feels very much that he is in the right place at the right time of his career."

Martinez expects Barkley to excel for Roy Hodgson's side in Brazil, with his big-game mentality and adaptability to a range of positions offering the England manager greater options in midfield.

"If you analyse Ross's season it's been against the top teams when he's excelled," he said. "Nothing is going to faze him. I do think there are certain types of games that will suit him better than others but he is ready to fulfil whatever role the England manager wants to give him.

"Ross could be in a position to impress millions of people at the World Cup but he will never look at it in that way. He will look at it in a humdrum manner, trying to be as good as he can and trying to help England as well as he can.

"He will come back the same person, I can guarantee you that. He's not someone who will lose sight of reality when he comes back."